这个结构体主要是用来link两个filter的，它存在于每个AVFilterContext中

struct AVFilterContext {const AVClass *av_class;        ///< needed for av_log() and filters common optionsconst AVFilter *filter;         ///< the AVFilter of which this is an instancechar *name;                     ///< name of this filter instanceAVFilterPad   *input_pads;      ///< array of input padsAVFilterLink **inputs;          ///< array of pointers to input linksunsigned    nb_inputs;          ///< number of input padsAVFilterPad   *output_pads;     ///< array of output padsAVFilterLink **outputs;         ///< array of pointers to output linksunsigned    nb_outputs;         ///< number of output padsvoid *priv;                     ///< private data for use by the filterstruct AVFilterGraph *graph;    ///< filtergraph this filter belongs to...}

结构体

先看结构体定义

/*** A link between two filters. This contains pointers to the source and* destination filters between which this link exists, and the indexes of* the pads involved. In addition, this link also contains the parameters* which have been negotiated and agreed upon between the filter, such as* image dimensions, format, etc.** Applications must not normally access the link structure directly.* Use the buffersrc and buffersink API instead.* In the future, access to the header may be reserved for filters* implementation.*/
struct AVFilterLink {AVFilterContext *src;       ///< source filterAVFilterPad *srcpad;